[0001] The present invention relates to a gear selection and engagement device designed
for assembly on a motor vehicle transmission of the type comprising a number of gears
moved axially by corresponding control forks, each of the said gears being designed
to be moved into such a position as to mesh with another axially-fixed gear, so as
to form a gear pair with a preset transmission ratio. one aim of the present invention
is to provide a gear selection and engagement device for use on the abovemention ed
type of transmission, the said device comprising a sin gle moving control shaft designed
to shift the said forks which are needed for both gear selection and engagement. Another
aim of the present invention is to provide a device of the abovementioned type designed
to control a large number of forks and, therefore, employable on trans missions with
a particularly large number of gears, e.g. the transmission on an industrial vehicle.
A further aim of the present invention is to provide a highly compact device ensuring
smooth, reliable operation.
[0002] With these aims in view, the present invention relates to a gear selection and engagement
device for a motor vehicle transmission comprising a number of axially-moving gears,
each designed to be moved into such a position as to mesh with another axially-fixed
gear so as to form a gear pair with a preset transmission ratio, the said axially-moving
gears being controlled by corresponding axially-moving control forks, characterised
by the fact that the said device comprises a shaft moving in the direction of and
round its own axis in relation to the transmission case by means of manually-operated
control means, the said shaft constituting a support for a number of hubs each integral
with a corresponding fork; a first set of teeth projecting radially from the said
shaft and being axially and torsionally integral with the same and one of the said
hubs being arranged between two adjacent teeth on the said first set; a second set
of teeth projecting radially from the said shaft, being tor sionally integral with
it and axially fixed in relation to the said case and one of the said hubs being arranged
between two adjacent teeth on the said second set; each- of the said hubs having at
least one pair of axial grooves designed to accommodate teeth on the said first and
second sets when the said shaft is shifted axially by the said control means so as
to prevent the relative hubs from moving as a consequence of the said axial displacement;
the said grooves being arranged round the circumference of each hub in such a preset
manner that, for a preset angular position of the said shaft corresponding to a preset
gear selection, all the teeth in the first set are aligned axially with corresponding
grooves on the said hubs, with the exception of the teeth adjacent to a preset hub
belonging to the fork which must be shifted axially for engaging the said preset gear,
so that, following subsequent axial displacement of the said shaft, only the said
hub preset for engaging the said gear is shifted axially by one of the said adjacent
teeth in the said first set; with the said shaft in the said angular position, the
second set teeth adjacent to the said preset hub being aligned with the corresponding
grooves on the hub and all the other said second set teeth being arranged essentially
contacting the other hubs, so as to prevent the said hubs from moving axially during
axial displacement of the said hub selected for engaging the said gear.
[0003] one arrangement of the present invention will now be described, by way of a non-limiting
example, with reference to the attached drawings in which :
- Fig.1 shows a view in perspective of the gear selection and engagement device according
to the present invention;
- Fig.2 shows a side view of the device;
- Fig.3 shows a cross section of the Fig.2 device along line III-III;
- Fig.4 shows an axial longitudinal section of the device;
- Fig.s 5 and 6 show two cross sections of the device, as in Fig.4, but in two different
operating positions corres ponding to the engagement of two different gears.
[0004] The device covered by the present invention is designed for use on a motor vehicle
transmission (not shown) comprising a number of axially-moving gears, each designed
to be moved by a corresponding fork (
1) into such a position as to mesh with another axially-fixed gear, so as to form a
gear pair with a preset transmission ratio. In the arrangement shown, the device is
privided with three such forks designed to shift corresponding gears axially in two
opposite directions.
[0005] The device comprises a shaft (2) moving in the direction of and round its own axis
in relation to the transmission case. For such a purpose, as shown in Fig.2, the end
sections (2a, 2b) of the said shaft are housed in correspond ing bearings of walls
3 on the said case. Shaft
2 constitutes a support for a number of hubs (4,
5, 6) each integral with a corresponding fork (
1) as shown clearly in Fig.
l. The said hubs are thus free to move axially and to turn in relation to the centre
part (7) of shaft
2, the said centre part (7) being greater in diameter than end sections
2a and
2b on the shaft.
[0006] The device also comprises a first set of teeth projecting radially from shaft 2 and
both axially and torsionally integral with it. The said teeth are arranged on the
shaft so that one of hubs 4, 5 or 6 fits between two adjacent teeth. Consequently,
in the arrangement shown, which provides for only three hubs, the teeth are four in
number (8, 9, 10, 11) as shown clearly in the Fig.
4 section. For conveniently forming the said teeth, provision is made for key
14 housed inside a corresponding annular groove (
15) in the centre part (7) of shaft 2. The said teeth project from the same side of
the said key the base section of which is housed in the said groove.
[0007] The device also comprises a second set of teeth also pro jecting radially from the
centre part (7) of shaft 2 and being torsionally integral with the shaft and fixed
axially in relation to the transmission case. As on the first set of teeth, one of
hubs 4, 5 or 6 is arranged between two adjacent teeth on the said second set. In the
arrangement shown, the said radial teeth are five in number (16, 17, 18, 19, 20) as
shown clearly in the Fig.4 section. As in the case of the first set, the teeth in
the said second set may also be formed by means of a key (21) also housed in a corresponding
longitudinal groove (2
2) on the centre part (7) of shaft
2, the said teeth projecting from one side of the key and the base section of the latter
being housed in the said groove.
[0008] To fix the teeth in the said second set axially in relation to the transmission case,
end teeth 16 and 2
0 of key
21 rest against the surfaces of case 3, whereas, to enable axial movement of shaft
2 in relation to the key, which is fixed axially, the latter is allowed to slide inside
the corresponding groove 2
2.
[0009] Each hub 4, 5 and 6 is provided with at least one pair of axial grooves (
25) each designed to accommodate, in the manner described hereafter, teeth in both the
first and second set, when shaft
2 is displaced axially. Axial displacement and rotation of shaft 2 are controlled by
control means, indicated as a whole by number
26, and comprising a first bushing (27), integral with shaft 2, and a second bushing
(
28), integral with a control bar (
29) arranged essentially perpendicular to shaft 2. The said two bushings are connected
by means of an essential ly spherical coupling (30) comprising a head (3
1) integral with bushing 28 and connected between a pair of tabs (3
2) integral with bushing 27. The side surfaces of the said head are conveniently cylindrical
and designed to rest on corresponding flat surfaces of tabs 32. Furthermore, a pin
(33) (Fig.
1) inserted inside the tabs fits through a slot (34) on head 31. Obviously, therefore,
with such a construction arrangement, each rotation of control bar 29 round its own
axis is accompanied by axial traversing of shaft 2, whereas, traversing of the said
bar is accompanied by rotation of the said shaft. Grooves
25 on each hub
4,
5 and 6 are arranged round the circumference of the relative hub in such a preset manner
that, for a preset angular position of shaft
2 corresponding to a preset gear selection, all the teeth in the first set are essentially
aligned with corresponding grooves on the said hubs, with the exception of the teeth
adjacent to a preset hub belonging to the fork which must be displaced axially for
engaging the said preset gear. In the arrangement shown, for the preset angular position
of shaft
2 shown in Fig.4, each of hubs-5 and 6 is provided on opposite sides of each with a
pair of grooves (25) designed to align with teeth 9, 10 and 11, as shown clearly in
Fig.
4, whereas no groove is provided on hub 4 for aligning with teeth 8 and 9.
[0010] Grooves 2
5 on each hub are arranged in such a manner that, with shaft
2 in the abovementioned angular position, the teeth in the second set are aligned with
corresponding grooves (
25) on the only hub to be displaced for engaging the preset gear, whereas all the other
teeth in the said second set are arranged essentially contacting the other hubs, so
as to prevent axial displacement of the said hubs during axial displacement, in the
manner hereafter described, of the said preset hub. Consequent ly, in the arrangement
shown in Fig.4 and for the angular position of shaft
2 shown in the said Figure, grooves
25 are provided only on hub
4 in alignment with teeth
16 and
17 in the second set, whereas no groove
25 is provided on the other hubs (
5, 6) in alignment with the other teeth (18, 19, 20) in the said second set.
[0011] Clearly, the arrangement of grooves
25 on the hubs depends on the displacement envisaged for fork
1 and will become clearer from the following examination of the way in which the device
operates.
[0012] With reference to Fig.
4 showing the device covered by the present invention with none of the gears engaged,
assume a gear engagement is required, such engagement being performed by shifting
rightwards, in Fig.4, fork
1 on the left of the drawing. Axial traversing of control bar 29, which turns bushing
27 and, consequently, also shaft 2, moves shaft
2 into the angular position shown in Fig.
4 in which teeth 9, 10 and 1
1 in the first set are aligned with corresponding grooves
25 on hubs 5 and 6. Axial displacement of the control bar thus serves to select a preset
gear.
[0013] In the abovementioned preset gear selection arrangement, teeth 18, 19 and 20 in the
second set are arranged essentially on each side of hubs
5 and 6, thus locking them axially and preventing any displacement during the following
engagement operation. The latter is achieved by turning control bar 29 which is accompanied
by axial traversing of bushing 27 and, consequently, also of shaft 2. If such rotation
is anticlockwise in Fig.4, it is accompanied by rightward displacement (Fig.4) of
the shaft (Fig.5) during which tooth 8 shifts hub 4 in the same direction, whereas
teeth 9 and 10 simply fit into the corresponding grooves (25) on respective hubs 5
and 6. Clearly, therefore, during such displacement, corresponding to actual engagement
of one of the gears, only the hub involved in the said engagement is displaced while
the others are locked in the idle position by the teeth in the second set.
[0014] If another gear is to be engaged, however, such engagement being achieved by shifting
leftwards fork 1 on the left of Fig.4, the selection arrangement is the same as that
already described whereas, for engaging the gear, control bar 29 is turned clockwise
in Fig.4 so as to shift shaft 2 and, consequently, also hub 4 leftwards in Fig.4.
[0015] This new engagement set-up is shown in Fig.6. As this clearly shows, during such
displacement, teeth
10 and 11 in the first set fit into corresponding grooves 25 on corresponding hubs
5 and 6 which are locked firmly in the idle position by the teeth in the second set.
[0016] A different gear selection may be achieved by turning shaft 2 into an angular position
other than the one already described. This new position may correspond to such a preset
arrangement of grooves
25 on the three hubs (4, 5, 6) as to determine, following axial displace ment of the
shaft, axial displacement of another fork in a preset direction or the simultaneous
displacement of two of the said forks.
[0017] Obviously, by providing each hub (4,
5, 6) with an appropriate number of grooves (2
5), the axial displacement of one or more hubs may be controlled while, at the same
time, locking the others axially.
[0018] To those skilled in the art it will be clear that changes can be made to the arrangement
described of the present invention, both in terms of form and arrangement of the various
parts involved, without, however, departing from the scope of the present invention.
1) - Gear selection and engagement device for a motor vehicle transmission comprising
a number of axially-moving gears, each designed to be moved into such a po sition
as to mesh with another axially-fixed gear so as to form a gear pair with a preset
transmission ratio, the said axially-moving gears being controlled by corres ponding
axially-moving control forks, characterised by the fact that the said device comprises
a shaft moving in the direction of and round its own axis in relation to the transmission
case by means of manually-operated control means, the said shaft constituting a support
for a number of hubs each integral with a corresponding fork; a first set of teeth
projecting radially from the said shaft and being axially and torsionally integral
with the same and one of the said hubs being arranged between two adjacent teeth on
the said first set; a second set of teeth projecting radially from the said shaft,
being torsionally integral with it and axially fixed in relation to the said case
and one of the said hubs being arranged between two adjacent teeth on the said second
set; each of the said hubs having at least one pair of axial grooves designed to accommodate
teeth on the said first and second sets when the said shaft is shifted axially by
the said control means so as to prevent the relative hubs from moving as a consequence
of the said axial displacement; the said grooves being arranged round the circumference
of each hub in such a preset manner that, for a preset angular position of the said
shaft corresponding to a preset gear selection, all the teeth in the first set are
aligned axially with corresponding grooves on the said hubs, with the exception of
the teeth adjacent to a preset hub belonging to the fork which must be shifted axially
for engaging the said preset gear, so that, following subsequent axial displacement
of the said shaft, only the said hub preset for engaging the said gear is shifted
axially by one of the said adjacent teeth in the said first set; with the said shaft
in the said angular position, the second set teeth adjacent to the said preset hub
being aligned with the corresponding grooves on the hub and all the other said second
set teeth being arranged essentially contacting the other hubs, so as to prevent the
said hubs from moving axially during axial displacement of the said hub selected for
engaging the said gear.
2) - Device according to Claim 1, characterised by the fact that the said teeth in the said first set are formed on
a key inserted inside a first axial groove on the said shaft.
3) - Device according to Claim 1 or 2, characterised by the fact that the said teeth
in the said second set are formed on a key inserted inside a second axial groove on
the said shaft, the said second key moving axially in re lation to the said shaft
and being locked axially in relation to the said case.
4) - Device according to one of the foregoing Claims, cha racterised by the fact that
the said manually-operated control means comprise a first rotary bushing, coaxial
and integral with the said shaft and provided with an axial groove for the teeth in
the said second set, the said first bushing being connected, by means of an essen
tially spherical coupling, to a second bushing integral with a control rod turning
round and moving in the direction of its own axis, perpendicular to that of the said
shaft, the said axis being arranged in such a manner that axial traversing of the
said rod controls rotation of the said shaft for gear selection, whereas rotation
of the said rod controls axial traversing of the said shaft for engaging the said
gear.
5) - Device according to one of the foregoing Claims, cha racterised by the fact that
the said first and said second groove on the said shaft lie in the same diametrical
plane on the said shaft and in diametrically opposed positions.